1. Field of the Invention
The present invention relates to a coal shaver with cutter fronts, comprised of shearing blades and bottom blades at both ends of the coal shaver, for extraction work in both shaver cutting directions, whereby the shearing blades are attached to the shaver body and the bottom blades are attached to the shanks, which are arranged to be adjustable and lockable in the guides, provided for at the shaver body.
2. The Prior Art
In one coal shaver known in the art (German patent specifications Nos. 13 00 889, 19 43 016, 22 50 535 and 25 00 680) the shearing blades are graduated one after the other from bottom to top at both ends, respectively, of the coal shaver. The shearing blades form a ramp-like ascending plane on which the loosened coal to be found in the shaver gap is raised to the upper edge of the side profile of the conveyer so that the coal can be loaded into the conveyer. Each main group of chisels has a bottom blade set in front, which is attached to a circular shaped sliding segment. The sliding segments are arranged to pivot in the corresponding circularly shaped guide, located below the main groups of chisels of the shaver body so that the cutting depth of the bottom blade can be adjusted.
In this known coal shaver, the bottom blade can be set at different angles to the cutting direction, depending on the altitude level of the coal shaver, so that the the resulting release and thrust force, acting on the bottom blade, results in a lateral force on the shank and thus results in a flexural moment on the curved shank. This is sometimes the reason for fractures observed in the bottom blade shank.
Another shaver known in the art (German specification No. 28 19 082) has flapper-type tool holders with shearing blades, which are arranged to pivot on axes, rotating in the longitudinal direction of the flapper-type coal holders; the blades are attached to the holders, which are on both sides of the shaver body. With respect to the shearing blades, working in the same direction of shaver travel, the bottom blades are set so far back that in every direction of shaver travel the bottom blade, which is put into operating position, is at the rear end of the plane near the shearing blades, which are idle in the rear.